深埋藏条件下鲕粒灰岩的热水交代实验研究

在相对静岩压力40 MPa、地温150℃(大体相当于4 000 m深埋条件)、用时15 d的条件下,对灰色中厚层状鲕粒灰岩进行深埋藏热水交代白云化实验研究。结果表明:反应前后岩石的结构发生了轻微变化,尾液中的主要化学成分Ca2+浓度从0 mg/L增加到337 mg/L,Mg2+浓度从过饱和溶液降低到2 830 mg/L。电子探针分析结果表明,固体样CaO含量由61.000%降为60.830%,而MgO则由0.296%升到0.350%。可见,参与实验的固、液样品反应前后主量元素Ca、Mg有一定的变化。但根据样品的宏观观察、镜下鉴定、扫描电镜及X衍射图谱的综合对比,认为在该实验条件下,尚未产生明显的白云化现象。     

Linking early diagenesis and sedimentary facies to sequence stratigraphy on a prograding oolitic wedge: The Bathonian of western France (Aquitaine Basin)

To improve the understanding of the distribution of reservoir properties along carbonate platform margins, the connection between facies, sequence stratigraphy, and early diagenesis of discontinuities along the Bathonian prograding oolitic wedge of the northeastern Aquitaine platform was investigated. Eight facies are distributed along a 50 km-outcropping transect in (1) toe-of-slope, (2) infralittoral prograding oolitic wedge, (3) platform margin (shoal), (4) open marine platform interior, (5) foreshore, and (6) terrestrial settings. The transition from shallow platform to toe-of-slope facies is marked in the field by clinoforms hundred of meters long. Carbonate production was confined to the shallow platform but carbonates were exported basinward toward the breakpoint where they cascaded down a 20–25° slope. Ooid to intraclast grainstones to rudstones pass into alternating marl-limestone deposits at an estimated paleodepth of 40–75 m. Three sea-level falls of about 10 m caused the formation of discontinuities corresponding to sequence boundaries. Along these discontinuities, erosional marine hardgrounds formed in a high-hydrodynamic environment at a water depth of less than 10 m, displaying isopachous fibrous cements and meniscus-type cements. The cements pass landward into meniscus and microstalactitic forms along the same discontinuities, which are characteristic of subaerial exposure. During the deposition of transgressive systems tracts, carbonate accumulation remained located mostly on the shallow platform. Energy level increased and carbonates were exported during the deposition of highstand systems tracts forming the infralittoral prograding oolitic wedge. During the deposition of lowstand systems tracts, carbonate production fell to near zero and intraclast strata, derived from the erosion of hardgrounds on the shallow platform, prograded basinward. Early diagenetic cements are related exclusively to discontinuities that are not found within the prograding wedge because of the continuous high sedimentation rate under lower hydrodynamic conditions. This absence of early cementation within the infralittoral prograding oolitic wedge was conducive to porosity conservation, making such features good targets for carbonate reservoir exploration. This study proposes a novel sequence stratigraphy model for oolitic platform wedges, including facies and early diagenesis features.     

Diamictite and oolitic ironstones, a sedimentary association at Ordovician–Silurian transition in the north Gondwana margin: New evidence from the inner nappe of Sardinia Variscides (Italy)

The contact between the Silurian black phyllite and the Cambro–Ordovician underlying rocks has been investigated over different tectonic units, affected by green-schist facies metamorphism, in the inner nappe zone of the Sardinia Variscides. In spite of strain and metamorphism, the field work highlighted the occurrence of diamictic sediments. In the Canaglia Tectonic Unit the diamictite consists of dark, massive metamorphic claystone bearing chamositic ooliths, chamositic nodules and millimetre to centimetre sized clasts, dispersed, or gathered in clusters, within the muddy matrix. In the Argentiera Tectonic Unit the diamictite consists of angular clasts, ranging in size from few millimetres to several decimetres, scattered within a finely laminated black sericitic meta-argillite. Field data, textural and compositional analyses suggest a glacio-marine environment for the formation of the diamictites.

The Canaglia diamictite deposited in a protected, glacial-influenced, shore. Compositionally it can be defined as ironstone; in the Upper part it hosts a horizon of clast-supported conglomeratic hard ironstone, mostly made of magnetite, which testifies for sub-aerial reworking. The source of the iron is to be related to local, glacio-eustatic driven, emergence of Upper Ordovician alkaline mafic volcanics. These are widespread in the uppermost Ordovician of the Canaglia Unit, possibly linked to the rifting stage that invested the north Gondwana margin, before the uppermost Ordovician–early Silurian sea level rise.

The Argentiera diamictite deposited beyond the iron-rich diamictite in the outer euxinic shelf that was reached by rain out of rafted debris.     

鄂西高磷鲕状赤铁矿磁化还原矿物组成及分布规律

鄂西高磷鲕状赤铁矿原矿全铁品位47.56%,含P 0.93%,主要脉石矿物为绿泥石、磷灰石、石英、方解石、铁白云石,属难选铁矿石。通过磁化焙烧-磨矿-磁选优化工艺,最佳磁化焙烧条件为:焙烧温度800℃、焙烧时间90min、还原剂用量12%,焙烧矿磨矿细度-0.074mm占85.15%,经弱磁选可得到全铁品位为58.13%、磷含量0.70%,铁回收率为90.41%的粗精矿。对磁化焙烧-磁选过程的各产物组成分析表明,焙烧矿和粗精矿中主要矿物为磁铁矿,占比分别为65%和85%;主要脉石矿物为绿泥石、磷灰石、石英、铁白云石等。粗精矿矿物的嵌布粒度较细,-0.074mm粒级占85.15%,但部分矿物仍以相互浸染、包裹、鲕状碎屑、连晶等形式存在,矿物仍未完全单体解离,从而导致粗精矿中杂质磷、铝等含量较高。粗精矿细磨后粒度-0.022mm含量为80%时,磁铁矿的解离度为84.63%,可实现磁铁矿充分单体解离,经过深选可提高铁精矿质量。     

古海相致密碳酸盐岩储层描述技术——以川东南涪陵南部地区飞仙关组三段鲕粒灰岩为例

针对涪陵南部低钻探程度区,以层序地层、沉积相等研究为主,地震参数为辅的技术思路开展储层描述。基础研究表明,涪陵南部地区与鄂西渝东建南地区处于同一个缓坡高能沉积相带内。利用层系地层学建立飞三段鲕滩发育模式,结合前人对飞三段鲕滩储层响应特征描述、建南地区jian35井飞三段鲕滩储层地震响应特征分析及模型正演,开展研究区飞三段鲕滩储层响应特征分析,总结出涪陵南部飞三段鲕滩储层具有叠置迁移的“亮点”响应特征。进一步结合地震相、地震属性及地震反演,落实出涪陵南部飞三段鲕滩储层有利分布区。     

四川盆地东北部飞仙关组高效气藏形成机理

最近10年,四川盆地东北地区发现了一批飞仙关组鲡滩高效气藏。本文通过对大量实验测试数据的分析整理以及成藏过程的模拟研究,提出了高效气藏形成机理。指出古油藏及分散液态烃在燕山中期快速升温条件下,形成高效气源灶,为高效气藏的形成提供了丰富的气源;优质鲡粒白云岩储集层经历6个阶段的演化历史,受控于沉积相带、烃类充注、深埋藏条件下强烈溶蚀以及多期断层活动;二叠系烃源岩与飞仙关组储集层存在强大的剩余压力差,为油气沿断层发生优势输导提供强大动力;燕山晚期-喜马拉雅期的构造作用,使得气藏发生调整与改造。     

A new sediment type of coated grain: Oolitic sinter

As a special sedimentary grain type, the coated grain (with an ooid model) has been known for two centuries due to its fascinating special fabric and genesis developments. The leading factors in forming the coated grain consist mainly of: (1) microorganism movement field; (2) chemical sedimentary effect; (3) hydrodynamic force environment and topography condition; (4) abundant core material supply; (5) embedding condition; and (6) humic acids condition in water medium. With the development of the coated grain genesis, the single factor theory cannot reasonably explain the exact formation of the surface sediment of coated grain. Here, we find a new way to study the coated grain on the basis of traditional research methods. The Wenquan area on the northeast edge of the Qiangtang Basin is one of the few areas where the coated grain is developing, and is a rare “natural laboratory” for the study of the coated grain and the thermal spring sediment. The oolitic sinter of the area has the triaxiality modality of pea polymer, and is obviously different from the karst travertine and the normal lacustrine ooid. We found that the hot spring water in the Wenquan area has higher partial pressure of CO₂ \(\left( {P_{CO_2 } } \right)\) and saturation index of the calcite (SI_c) than normal. Macrocosmically, the oolitic sinter is shaped like a pea, and its grains and gap fillings are light yellow. Microcosmically, the sinter grain forms six types of fundamental lamina, and those six types are developed to be four grain types with different combinations. The C-axis of the mineral grain of sinter cement (calcite) is normal to the lamina face, and grows on it with distinct generation formations. In short, the grain type of oolitic sinter is the oncoid, with the grain development caused by the factors such as the shallow water of strong hydrodynamic force, the special hydrochemistry condition, and the extensive algae activities (diatom).     

Properties of Ironstone Lateritic Gravels in Relation to Gravel Road Pavement Construction

A laboratory investigation was conducted to determine properties of five samples of ‘oolitic ironstone’ lateritic gravel aggregates which are relevant to their use as road construction materials. Measured values of physico-chemical, physico-mechanical as well as index properties and compaction characteristics are similar to those of other lateritic, gravels occurring in West Africa which are used in road pavement applications. These lateritic clayey gravels have good workability as engineering construction materials and are rated fair to good as road aggregates in terms of probable in-situ behaviour based on water absorption values. Relationships between maximum dry unit weight and optimum moisture content as well as those between California bearing ratio and some derived soil parameters such as grading modulus, plasticity product or plasticity modulus can be described using a third-order polynomial function. The maximum dry unit weight has a bimodal frequency distribution and can be predicted from logarithm to base 10 of compaction energy with fairly good accuracy.     

川东北飞仙关组鲕滩储层硫酸溶蚀的证据和模式探讨

川东北飞仙关组鲕滩储层的主要储集空间为溶蚀孔洞,主要由大气淡水溶蚀作用、有机酸溶蚀作用和硫酸溶蚀作用所形成。通过硫酸对灰岩和白云岩溶蚀实验、天然气中硫化氢含量与飞仙关组石膏厚度关系分析、天然气中硫同位素与地层中的硫同位素比较、方解石胶结物的阴离子分析等证据,首次提出了硫酸溶蚀在该储层形成中起很重要的作用。探讨了硫酸溶蚀形成储层的模式。     

蜀南地区飞仙关组鲕滩储层成因机制分析

对蜀南地区飞仙关组鲕滩储层的深入研究表明,飞仙关组鲕滩储层储集空间以大气淡水选择性溶蚀形成的铸模孔和粒内溶孔为主,储层发育在滩体中上部,具有明显的层位性。结合沉积期古地貌、海平面升降变化、古气候及成岩演化等储层控制因素分析认为,该区鲕滩储层为早期岩溶成因,早期大气淡水淋溶是针孔鲕粒灰岩储层形成的关键。海底古地貌高地鲕粒滩为储层的形成和发育提供了物质基础,决定了早期孔、渗层的时空分布规律;沉积期古地貌、海平面变化及古气候决定了早期岩溶的强度,控制了储层发育程度。埋藏溶蚀和构造破裂对储层具有一定的优化改造作用,但作用有限。